JP4390004B2 - Internal high-hardness pearlite steel rail with excellent wear resistance and fatigue damage resistance and method for producing the same - Google Patents

Description

  The present invention relates to an internal high-hardness pearlite steel rail excellent in wear resistance and fatigue damage resistance, and a method for manufacturing the same, and more particularly, in a severe mine railway such as an overseas mining railway having a heavy freight car weight and many sharp curves. The present invention relates to an internal high-hardness pearlite steel rail excellent in wear resistance and fatigue damage resistance that achieves a long life of a rail used under high axial load conditions, and a manufacturing method thereof.

  In high-axle heavy railways, mainly transporting ore, the load on the axles of freight cars is much higher than that of passenger cars, and the use environment of the rails is also severe. Conventionally, steel having a pearlite structure has been used as a rail used in such an environment from the viewpoint of placing importance on wear resistance. However, in recent years, the load on a freight car has been further increased in order to increase the efficiency of transportation by rail, and further improvements in wear resistance and fatigue damage resistance are required. The high-axle railway is a railway having a large load weight of trains and wagons (a load weight per freight car is about 150 tons or more, for example).

  In recent years, various studies have been conducted with the aim of further improving wear resistance. For example, in Patent Document 1 and Patent Document 2, the C amount is increased from 0.85% by mass to 1.20% by mass or less, and in Patent Document 3 and Patent Document 4, the C amount is increased from 0.85% by mass to 1.20% by mass and the rail head. Some devices have been devised such as increasing the amount of C and increasing the cementite fraction to improve the wear resistance, such as by heat-treating the part.

  On the other hand, the rails in the curved section of the high-axle heavy railway are subjected to rolling stress due to wheels and sliding force due to centrifugal force, so that wear of the rail becomes more severe and fatigue damage due to sliding occurs. As described above, when the C content is simply over 0.85% by mass and not more than 1.20% by mass, a pro-eutectoid cementite structure is formed depending on the heat treatment conditions, and the amount of the cementite layer in the brittle pearlite layered structure increases. Improvement is not expected. Therefore, Patent Document 5 proposes a technique for suppressing the formation of pro-eutectoid cementite by adding Al and Si and improving the fatigue damage resistance. However, it was difficult to satisfy both wear resistance and fatigue damage resistance in steel rails having a pearlite structure, such as the addition of Al, which generates oxides that cause fatigue damage.

In order to improve the service life of the rail, in Patent Document 6, the Vickers hardness in the range of at least 20mm in depth is set to Hv370 or more starting from the surface of the head corner and the top of the rail. The service life is improved. Further, in Patent Document 7, by controlling the pearlite block, the hardness of at least a depth of 20 mm starting from the surface of the head corner and the top of the rail is in the range of Hv300 to 500. The service life of the rail is improved.
Japanese Patent Laid-Open No. 8-109439 Japanese Patent Laid-Open No. 8-144016 JP-A-8-246100 JP-A-8-246101 Japanese Patent Laid-Open No. 2002-69585 Japanese Patent Laid-Open No. 10-195601 JP2003-293086

However, the usage environment of pearlite steel rails has become more severe, and in order to improve the service life of pearlite steel rails, it has been a challenge to further increase the hardness and extend the range of hardening depth. The present invention has been made to solve this problem. Compared with conventional hypoeutectoid, eutectoid and hypereutectoid pearlite steel rails, the addition of Si, Mn and Cr is optimized and hardenability is improved. By optimizing the index (hereinafter referred to as DI) and the carbon equivalent (hereinafter referred to as C _eq ), at least the rail top surface is used as a starting point to increase the hardness within the 25 mm depth range, and wear and fatigue resistance. An internal high-hardness pearlitic steel rail excellent in both damage characteristics is provided together with a preferable manufacturing method thereof.

In order to solve the above-mentioned problems, the inventors manufactured a pearlite steel rail in which the contents of Si, Mn, and Cr were changed, and intensively investigated the structure, hardness, wear resistance, and fatigue damage resistance. As a result, the [% Mn] / [% Cr] value calculated from the Mn content [% Mn] and the Cr content [% Cr] is set to 0.3 or more and less than 1.0, so that the lamellar layer of the pearlite layer (hereinafter, simply referred to as “lamellar”). (Also known as lamellar) The internal space of the rail head defined by the hardness in the range of at least 25mm depth from the surface layer of the rail head becomes Hv380 or more and less than Hv480, wear resistance and fatigue damage resistance Found to improve. Further, the hardenability index (ie DI value) is in the range of 5.6 to 8.6, the carbon equivalent (ie C _eq value) is in the range of 1.04 to 1.27, Mn content [% Mn], Cr content [% Cr], Wear resistance and fatigue damage resistance are improved by keeping the value of [% Si] + [% Mn] + [% Cr] calculated from the Si content [% Si] within the range of 1.55 to 2.50 mass%. It was found that the effect to be able to be maintained stably.

The present invention has been made based on these findings.
That is, the present invention includes C: 0.73-0.85 mass%, Si: 0.5-0.75 mass%, Mn: 0.3-1.0 mass%, P: 0.035 mass% or less, S: 0.0005-0.012 mass%, Cr: 0.2-1.3 mass% %, With the balance being Fe and inevitable impurities, Mn content is [% Mn], Cr content is [% Cr], and [% Mn] / [% Cr] value is 0.3 or more It is an internal high hardness type pearlite steel rail having an internal hardness of the rail head defined by Vickers hardness in a range of at least 25 mm depth from the surface layer of the rail head that is less than 1.0 and is Hv380 or more and less than Hv480.

In the internal high hardness type pearlite steel rail of the present invention, the C content of the above composition is [% C], the Si content is [% Si], the Mn content is [% Mn], and the P content is [%]. The P value, S content is [% S], Cr content is [% Cr], the DI value calculated by the following formula (1) satisfies the range of 5.6 to 8.6, and the following (2 It is preferable that the C _eq value calculated by the above formula satisfies the range of 1.04 to 1.27.
DI = (0.548 [% C] ^1/2 ) × (1 + 0.64 [% Si]) × (1 + 4.1 [% Mn])
× (1 + 2.83 [% P]) × (1−0.62 [% S]) × (1 + 2.23 [% Cr]) (1)
C _eq = [% C] + ([% Si] / 11) + ([% Mn] / 7) + ([% Cr] /5.8) (2)
Further, assuming that the Si content of the above composition is [% Si], the Mn content is [% Mn], and the Cr content is [% Cr], the [% Si] + [% Mn] + [% Cr] value is It is preferable to satisfy the range of 1.55 to 2.50% by mass. Further, in addition to the above composition, V: 0.001 to 0.30 mass%, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Nb: 0.001 to 0.05 mass%, and Mo: 0.5 mass% or less are selected. It is preferable to contain 1 type (s) or 2 or more types.

Further, in the internal high hardness type pearlite steel rail of the present invention, the lamellar spacing of the pearlite layer in the range of a depth of at least 25 mm from the surface layer of the rail head is preferably 0.04 to 0.15 μm.
In the present invention, the steel material having the above composition is hot-rolled into a rail shape so that the rolling finishing temperature is 850 to 950 ° C., and then the rail head is 1.2 to 5 ° C. above the pearlite transformation start temperature. This is a method for producing an internal high-hardness pearlite steel rail that is accelerated to 400 to 650 ° C. at a cooling rate of 1 sec.

  According to the present invention, it becomes possible to stably manufacture a pearlite steel rail having wear resistance and fatigue damage resistance far superior to those of a conventional pearlite steel rail. This contributes to the prolongation of service life and the prevention of railway accidents, and has an industrially beneficial effect.

The reasons for limiting the requirements including the composition of the internal high hardness pearlitic steel rail of the present invention will be described.
C: 0.73-0.85 mass%
C forms cementite in the pearlite structure and is an essential element for ensuring the wear resistance, and the wear resistance improves as the content increases. However, if it is less than 0.73 mass%, it is difficult to obtain excellent wear resistance as compared with the conventional heat treated pearlite steel rail. On the other hand, if it exceeds 0.85% by mass, pro-eutectoid cementite is formed at the austenite grain boundaries during transformation after hot rolling, and the fatigue damage resistance is remarkably reduced. Therefore, the C content is 0.73 to 0.85 mass%. Preferably it is 0.75-0.85 mass%.

Si: 0.5-0.75 mass%
Si needs to be 0.5% by mass or more as a deoxidant and a strengthening element of the pearlite structure. However, if it exceeds 0.75% by mass, the weldability deteriorates due to the high bonding strength with Si. Furthermore, due to the high hardenability of Si, a martensite structure is easily formed on the surface layer of the internal high hardness type pearlitic steel rail. Accordingly, the Si content is 0.5 to 0.75 mass%. Preferably it is 0.5-0.70 mass%.

Mn: 0.3 to 1.0 mass%
Mn contributes to increasing the strength and ductility of internal hardened rails by lowering the pearlite transformation temperature and reducing the lamellar spacing, but excessive addition reduces the equilibrium transformation temperature of pearlite, and as a result In other words, it is an element that reduces the degree of supercooling and coarsens the lamellar spacing. If the amount is less than 0.3% by mass, a sufficient effect cannot be obtained. If the amount exceeds 1.0% by mass, a martensite structure is likely to be formed, and the material is liable to be hardened or embrittled during heat treatment and welding. Further, even if a pearlite structure is formed, the equilibrium transformation temperature is lowered, leading to coarse lamellar spacing. Therefore, the amount of Mn is 0.3 to 1.0% by mass. Preferably it is 0.3-0.8 mass%.

P: 0.035% by mass or less
The content of P exceeding 0.035% deteriorates ductility. Therefore, the P content is 0.035% by mass or less. Preferably it is 0.020 mass% or less.
S: 0.0005 to 0.012 mass%
S is present in the steel material mainly in the form of A-based inclusions, but when it exceeds 0.012% by mass, the amount of inclusions increases remarkably, and at the same time, coarse inclusions are produced, so that the cleanliness of the steel materials deteriorates. On the other hand, when the content is less than 0.0005% by mass, the steelmaking cost is increased. Therefore, the S amount is set to 0.0005 to 0.012% by mass. Preferably it is 0.0005-0.010 mass%. More preferably, it is 0.0005-0.008 mass%.

Cr: 0.2-1.3 mass%
Cr is an element that raises the pearlite equilibrium transformation temperature and contributes to refinement of the lamellar spacing, and at the same time brings about further strengthening by solid solution strengthening. However, if the amount is less than 0.2% by mass, sufficient internal hardness cannot be obtained. On the other hand, if the amount exceeds 1.3% by mass, the hardenability becomes too high, martensite is generated, and the wear resistance and fatigue damage resistance decrease. . Therefore, the Cr content is 0.2 to 1.3 mass%. Preferably it is 0.3-1.3 mass%, More preferably, it is 0.5-1.3 mass%.

[% Mn] / [% Cr]: 0.3 or more and less than 1.0
Mn and Cr are elements added to increase the hardness of the internal hardened pearlite steel rail. However, if the balance between the Mn content [% Mn] and the Cr content [% Cr] is not appropriate, martensite is generated on the surface layer of the internal high hardness type pearlite steel rail. The unit of [% Mn] and [% Cr] is mass%. If the value of [% Mn] / [% Cr] is less than 0.3, the amount of Cr added increases, and because of the high hardenability of Cr, martensite is generated on the surface layer of the internal hardened pearlite steel rail. It becomes easy. In addition, when the value of [% Mn] / [% Cr] is 1.0 or more, the amount of Mn added increases, and because of the high hardenability of Mn, the surface layer of the internal high-hardness pearlite steel rail is similarly martensite. Is easier to generate. The content of Mn and Cr is within the above ranges, and the value of [% Mn] / [% Cr] is set to 0.3 or more and less than 1.0, thereby preventing the formation of martensite on the surface layer and rails. The internal hardness of the head (hardness in a range of at least 25 mm depth from the head surface layer of the internal high-hardness pearlitic steel rail) can be controlled within a range described later. Therefore, the value of [% Mn] / [% Cr] is 0.3 or more and less than 1.0. Preferably it is 0.3 or more and 0.9 or less.

DI: 5.6 to 8.6
DI value is C content [% C], Si content [% Si], Mn content [% Mn], P content [% P], S content [% S], Cr It is a value calculated by the following formula (1) with the content as [% Cr]. The units of [% C], [% Si], [% Mn], [% P], [% S], and [% Cr] are all mass%.
DI = (0.548 [% C] ^1/2 ) × (1 + 0.64 [% Si]) × (1 + 4.1 [% Mn])
× (1 + 2.83 [% P]) × (1−0.62 [% S]) × (1 + 2.23 [% Cr]) (1)
This DI value represents hardenability and is used as an index for determining the quality of hardenability. In the present invention, while suppressing the formation of martensite on the surface layer of the internal high hardness type pearlite steel rail, It is preferably used as an index for achieving the target value of the internal hardness of the rail head and maintained within a suitable range. When the DI value is less than 5.6, the desired internal hardness can be obtained, but it is close to the lower limit of the target hardness range, and therefore further improvement in wear resistance and fatigue damage resistance cannot be expected. On the other hand, if the DI value exceeds 8.6, the hardenability of the internal high-hardness pearlite steel rail is increased, and martensite is easily generated on the surface layer of the rail head. Therefore, the DI value is preferably 5.6 to 8.6. More preferably, it is 5.6 to 8.2.

C _eq : 1.04-1.27
The C _eq value is calculated by the following formula (2), where C content is [% C], Si content is [% Si], Mn content is [% Mn], and Cr content is [% Cr]. Value. The units of [% C], [% Si], [% Mn], and [% Cr] are all mass%.
C _eq = [% C] + ([% Si] / 11) + ([% Mn] / 7) + ([% Cr] /5.8) (2)
This C _eq value is used to estimate the maximum hardness and weldability obtained from the alloying ratio of the alloy components. In the present invention, however, the formation of martensite on the surface layer of the internal high-hardness pearlite steel rail is suppressed. At the same time, it is preferably used as an index for achieving the target value of the internal hardness of the rail head and maintained within a suitable range. If the C _eq value is less than 1.04, the desired internal hardness can be obtained, but it will be close to the lower limit of the target hardness range, so that further improvement in wear resistance and fatigue damage resistance cannot be expected. Further, when the C _eq value exceeds 1.27, the hardenability of the internal high-hardness pearlitic steel rail is increased, and martensite is easily generated on the surface layer of the rail head. Therefore, the C _eq value is preferably 1.04 to 1.27. More preferably, it is 1.04-1.20.

If the internal hardness of the rail head (hardness in the range of depth of at least 25mm from the surface of the head of the internal hardened pearlitic steel rail is at least 25mm deep) is less than Hv380 and less than Hv480, if the internal hardness of the rail head is less than Hv380, Abrasion is reduced and the service life of internal hardened pearlitic steel rails is reduced. On the other hand, when it becomes Hv480 or more, martensite is generated, and the fatigue damage resistance of the steel is lowered. Therefore, the internal hardness of the rail head is set to Hv380 or more and less than Hv480. Preferably it is more than Hv390 and less than Hv480. In addition, the definition of the internal hardness of the rail head is at least 25 mm deep from the top surface of the internal hardened pearlitic steel rail. This is because the wear resistance of the internal high-hardness pearlite steel rail is reduced and the service life is reduced.

[% Si] + [% Mn] + [% Cr]: 1.55 to 2.50 mass%
The sum of Si content [% Si], Mn content [% Mn] and Cr content [% Cr] (= [% Si] + [% Mn] + [% Cr]) is less than 1.55% by mass. If there is, it is difficult to satisfy the internal hardness of the rail head of Hv380 or more and less than Hv480. On the other hand, if it exceeds 2.50% by mass, a martensite structure is formed due to the high hardenability of Si, Mn, and Cr, and the ductility and toughness tend to decrease. Therefore, the [% Si] + [% Mn] + [% Cr] value is preferably 1.55 to 2.50 mass%. More preferably, it is 1.55-2.30 mass%. The units of [% Si], [% Mn], and [% Cr] are all mass%.

The composition is further selected from V: 0.001 to 0.30 mass%, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Nb: 0.001 to 0.05 mass%, and Mo: 0.5 mass% or less 1 A seed | species or 2 or more types may be added as needed.
V: 0.001 to 0.30 mass%
V forms a carbonitride, disperses and precipitates in the matrix, and improves the wear resistance. However, if it is less than 0.001% by mass, its effect is small, while if it exceeds 0.30% by mass, the workability deteriorates and it is manufactured. Cost increases. Moreover, since the alloy cost increases, the cost of the internal high hardness type pearlite steel rail increases. Therefore, when adding V, the amount of V is preferably 0.001 to 0.30 mass%. More preferably, it is 0.001-0.15 mass%.

Cu: 1.0% by mass or less
Cu, like Cr, is an element for further strengthening by solid solution strengthening. However, if it exceeds 1.0% by mass, Cu cracking tends to occur. Therefore, when adding Cu, it is preferable that the amount of Cu shall be 1.0 mass% or less. More preferably, it is 0.005-0.5 mass%.
Ni: 1.0% by mass or less
Ni is an element for increasing the strength without deteriorating the ductility. Moreover, in order to suppress Cu cracking by compounding with Cu, it is desirable to add Ni when Cu is added. However, addition exceeding 1.0% by mass increases the hardenability and produces martensite, which tends to decrease the wear resistance and fatigue damage resistance. Therefore, when adding Ni, the amount of Ni is preferably 1.0% by mass or less. More preferably, it is 0.005-0.5 mass%.

Nb: 0.001 to 0.05 mass%
Nb combines with C in the steel and precipitates as a carbide during and after rolling, and effectively acts to refine the pearlite colony size. As a result, the wear resistance, fatigue damage resistance, and ductility are greatly improved, which greatly contributes to the extension of the life of the internal hardened pearlite steel rail. However, if the Nb content is less than 0.001% by mass, it is difficult to obtain a sufficient effect. Moreover, even if it adds exceeding 0.05 mass%, the improvement effect of abrasion resistance and fatigue damage resistance will be saturated, and the effect corresponding to addition amount will not be acquired. Therefore, when Nb is added, the Nb amount is preferably 0.001 to 0.05% by mass. More preferably, it is 0.001-0.03 mass%.

Mo: 0.5% by mass or less
Mo is an element for further strengthening by solid solution strengthening. However, if it exceeds 0.5% by mass, a bainite structure is likely to occur, and the wear resistance tends to be lowered. Therefore, when adding Mo, the amount of Mo is preferably 0.5% by mass or less. More preferably, it is 0.005-0.3 mass%.

Lamella spacing of the pearlite layer in the range of at least 25mm depth from the top surface of the rail: 0.04-0.15μm
As for the lamellar spacing of the pearlite layer, the finer the inner hardened pearlite steel rail, the higher the hardness, which is advantageous from the viewpoint of improving wear resistance and fatigue damage resistance. Therefore, it is preferable that the thickness be 0.15 μm or less. In addition, if the lamellar spacing is to be less than 0.04 μm, a method of improving the hardenability and making it finer will be used. In this case, martensite is likely to be generated on the surface layer, and the fatigue damage resistance is adversely affected. Effect. Therefore, it is preferable to be 0.04 μm or more.

  In addition, a pearlite steel rail that contains other trace component elements within a range that does not substantially affect the effect of the present invention instead of a part of the remaining Fe in the composition according to the present invention is also included in the present invention. Belongs. Here, examples of the impurity include P, N, O and the like, and P can be allowed up to 0.035% by mass as described above. Further, N is allowable up to 0.006% by mass, and O is allowable up to 0.004% by mass. Furthermore, in this invention, Ti mixed as an impurity can be tolerated up to 0.0010 mass%. In particular, Ti forms an oxide and causes a reduction in fatigue damage resistance, which is a basic characteristic of the rail, and therefore it is preferable to control it to 0.0010% by mass or less.

  The internal high-hardness pearlitic steel rail of the present invention is obtained by hot rolling a steel material having the composition according to the present invention into a rail shape so that the rolling finishing temperature is 850 to 950 ° C., and subsequently at least the head of the rail-shaped body. Is preferably accelerated-cooled to a temperature of 400 to 650 ° C. at a cooling rate of 1.2 to 5 ° C./second from a temperature equal to or higher than the pearlite transformation start temperature. The reason why the rolling finishing temperature is 850 to 950 ° C., the cooling rate of accelerated cooling is 1.2 to 5 ° C./second, and the cooling stop temperature is 400 to 650 ° C. will be described below.

Rolling finishing temperature: 850-950 ° C
When the rolling finishing temperature is lower than 850 ° C., rolling is performed to a low temperature range of austenite, and not only processing strain is introduced into the austenite crystal grains, but also the degree of elongation of the austenite crystal grains becomes remarkable. The introduction of dislocations and an increase in the interfacial area of austenite grains increase the number of pearlite nucleation sites and the pearlite colony size becomes finer. Is coarsened and wear resistance is significantly reduced. On the other hand, when the rolling finishing temperature exceeds 950 ° C., the austenite crystal grains become coarse, so that the finally obtained pearlite colony size becomes coarse, and the fatigue damage resistance decreases. Therefore, the rolling finishing temperature is preferably 850 to 950 ° C.

Cooling rate from a temperature above the pearlite transformation start temperature: 1.2-5 ° C / sec. When the cooling rate is less than 1.2 ° C / sec, the pearlite transformation start temperature rises, the lamellar spacing of the pearlite layer becomes coarse, and wear resistance. Fatigue damage resistance is significantly reduced. On the other hand, when the cooling rate exceeds 5 ° C./second, a martensite structure is formed, and ductility and toughness are lowered. Therefore, the cooling rate is preferably in the range of 1.2 to 5 ° C./second. Preferably it is 1.2-4.6 degrees C / sec. Although the pearlite transformation start temperature varies depending on the cooling rate, in the present invention, it means the equilibrium transformation temperature, and in the component range of the present invention, a cooling rate in this range from 720 ° C. or higher may be adopted.

Cooling stop temperature: 400-650 ° C
In the case of the composition and cooling rate according to the present invention, in order to obtain a homogeneous pearlite structure at a cooling rate in the range of 1.2 to 5 ° C./sec, a cooling stop temperature of 70 ° C. or more lower than the equilibrium transformation temperature is secured. Is preferred. However, when the cooling stop temperature is less than 400 ° C., the increase in the cooling time leads to an increase in the cost of the internal high-hardness pearlite steel rail. Therefore, the cooling stop temperature is preferably 400 to 650 ° C. Preferably it is 450-650 degreeC.

Next, a method for measuring or evaluating wear resistance, fatigue damage resistance, internal hardness of the rail head, and lamellar spacing will be described.
(Abrasion resistance)
As for wear resistance, it is most desirable to actually lay an internal high-hardness pearlite steel rail for evaluation, but this requires a long time for the test. Therefore, in the present invention, the evaluation is performed by a comparative test that simulates the contact condition between an actual internal high hardness type pearlite steel rail and a wheel using a Nishihara type wear tester capable of evaluating the wear resistance in a short time. A Nishihara-type wear test piece 1 having an outer diameter of 30 mm is taken from the rail head and brought into contact with the tire test piece 2 and rotated for testing as shown in FIG. The arrows in FIG. 1 indicate the rotation directions of the Nishihara-type wear test piece 1 and the tire test piece 2, respectively. For the tire test piece, a round bar with a diameter of 32 mm was taken from the head of the normal rail described in JIS standard E1101, and it was heat-treated so that the Vickers hardness (load 98N) was Hv390 and the structure became a tempered martensite structure. After that, the shape shown in FIG. 1 was processed to obtain a tire test piece. The Nishihara-type wear test piece 1 is collected from two places on the rail head 3 as shown in FIG. A sample collected from the surface layer of the rail head 3 is a Nishihara type wear test piece 1a, and a sample collected from the inside is a Nishihara type wear test piece 1b. The center in the longitudinal direction of the Nishihara-type abrasion test piece 1b collected from the inside of the rail head 3 is located at a depth of 24 to 26 mm (average value 25 mm) from the upper surface of the rail head 3. The test environment is dry, and the amount of wear after 100,000 rotations is measured under the conditions of contact pressure: 1.4 Gpa, slip rate: −10%, rotation speed: 675 rpm (tire test piece is 750 rpm). A heat-treated pearlite steel rail is adopted as a reference steel material when comparing the amount of wear, and it is determined that the wear resistance is improved when the amount of wear is 10% or more less than this reference steel material. In addition, the wear resistance improvement allowance was calculated by [{(abrasion of reference material) − (amount of wear of test material)} / (amount of wear of reference material)] × 100.

(Fatigue damage resistance)
For fatigue damage resistance, the contact surface is a curved surface with a radius of curvature of 15 mm, a 30 mm diameter Nishihara-type wear test piece 1 is taken from the rail head, and brought into contact with the tire test piece 2 and rotated as shown in FIG. Perform the test. The arrows in FIG. 1 indicate the rotation directions of the Nishihara-type wear test piece 1 and the tire test piece 2, respectively. The Nishihara-type wear test piece 1 is collected from two places on the rail head 3 as shown in FIG. Since the position where the Nishihara type abrasion test piece 1 is collected and the position where the tire test piece is collected are the same as described above, the description thereof is omitted. The test environment is oil lubrication, contact pressure: 2.2Gpa, slip rate: -20%, rotation speed: 600rpm (tire test piece is 750rpm), the surface of the test piece is observed every 25,000 times, 0.5mm The rotation speed at the time when the above cracks are generated is defined as the fatigue damage life. Uses heat-treated pearlitic steel rail as a reference steel when comparing the fatigue damage life, and determines that fatigue resistance is improved when the fatigue damage time is 10% or longer than this reference steel. . In addition, the fatigue damage improvement allowance is [{(number of rotations until the occurrence of fatigue damage of the test material) − (number of rotations until the occurrence of fatigue damage of the reference material)} / (number of rotations until the occurrence of fatigue damage of the reference material) ] × 100.

(Internal hardness of rail head)
Measure the Vickers hardness in the range from the surface of the rail head to a depth of 25mm at a load of 98N and 1mm pitch. And the minimum value was made into the internal hardness of a rail head among all the hardness.
(Lamellar spacing)
Using a scanning electron microscope (SEM), the inside of any five fields of view is observed at a magnification of 7500 times for each of the vicinity of the surface of the rail head (about 1 mm deep) and the position of 25 mm deep. Further, when there is a portion having the narrowest lamellar interval, observation is performed at a magnification of 20000, and the lamellar interval in the field of view is measured. When there is no portion with a narrow lamellar interval in the field of view with a magnification of 7500 times, or when the cross section of the lamellar is not perpendicular to the lamellar surface but oblique, measurement is performed by switching to another field of view. The lamellar interval is evaluated by an average value of the measured lamellar intervals of 5 fields of view.

(Example 1)
The steel material having the composition shown in Table 1 was rolled and cooled under the conditions shown in Table 2 to produce a pearlite steel rail. Cooling was performed only on the rail head, and after cooling stopped, it was allowed to cool. The pearlite steel rail was evaluated for Vickers hardness, lamellar spacing, wear resistance and fatigue damage resistance. The results are shown in Table 3. The rolling finishing temperature in Table 2 indicates a value obtained by measuring the temperature of the rail head side surface layer on the final rolling mill entry side with a radiation thermometer as the rolling finishing temperature. The cooling stop temperature indicates a value obtained by measuring the temperature of the rail head side surface layer on the exit side of the cooling facility with a radiation thermometer as the cooling stop temperature. The cooling rate was defined as the time change in temperature from the start of cooling to the stop of cooling.

From these results, by setting the [% Mn] / [% Cr] value to 0.3 or more and less than 1.0, at least the 25mm range from the surface of the rail head becomes Hv380 or more and less than Hv480, and wear resistance and fatigue damage resistance are improved. It can be seen that it has improved. On the other hand, when the value of [% Mn] / [% Cr] is outside the range of 0.3 or more and less than 1.0, such as 1-L to 1-Q, the inside of the rail head (that is, the position at a depth of 25 mm from the surface layer) It can be seen that the hardness of the steel does not satisfy Hv380 or more and less than Hv480, wear resistance and fatigue damage resistance are reduced, or martensite is generated in the vicinity of the surface layer of the rail head and fatigue resistance is reduced. Further, in the invention examples, when the DI value satisfies 5.6 to 8.6 and the C _eq value satisfies 1.04 to 1.27, such as 1-B to 1-G and 1-S to 1-U, from 1-H It can be seen that the wear resistance and fatigue damage resistance are improved compared to 1-K. Furthermore, in the example of the invention, when the value of [% Si] + [% Mn] + [% Cr] cannot be controlled to 1.55 to 2.50% by mass like 1-R, the depth from the surface layer of the rail head is 25 mm. Although the hardness of the internal position satisfies Hv380 or more and less than Hv480, the properties of pearlite steel rails are better than those with [% Si] + [% Mn] + [% Cr] values controlled to 1.55 to 2.50 mass%. It turns out that it falls.

(Example 2)
The steel material having the composition shown in Table 4 was rolled and cooled under the conditions shown in Table 5 to produce a pearlite steel rail. Cooling was performed only on the rail head, and after cooling stopped, it was allowed to cool. The Vickers hardness, lamellar spacing, wear resistance and fatigue damage resistance of this pearlite steel rail were evaluated in the same manner as in Example 1. The results are shown in Table 6.

From these results, the addition amount of Si, Mn, Cr was optimized and the [% Mn] / [% Cr] value was 0.3 or more, such as 2-B to 2-J, 2-T to 2-V. Less than 1.0, [% Si] + [% Mn] + [% Cr] value is controlled to 1.55 to 2.50 mass%, and one or more selected from V, Cu, Ni, Mo It can be seen that the wear resistance and fatigue damage resistance are improved by adding the above component in an appropriate range. Further, among the inventive examples, the DI value is 5.6 to 8.6, and the C _eq value is 1.04, such as 2-B, 2-C, 2-E, 2-F, 2-J, 2-T to 2-V. It can be seen that by controlling to ˜1.27, wear resistance and fatigue damage resistance are improved as compared with 2-I from 2-D and 2-G. Furthermore, in the example of the invention, when the value of [% Si] + [% Mn] + [% Cr] cannot be controlled to 1.55 to 2.50% by mass as in 2-D and 2-I, the surface layer of the rail head Although the hardness at the position within 25mm from Hv380 is more than Hv380 and less than Hv480, it is pearlite steel compared with [% Si] + [% Mn] + [% Cr] value controlled to 1.55-2.50 mass%. It can be seen that the characteristics of the rail are degraded. Moreover, when Ti is added like 2-S, it turns out that fatigue damage resistance falls.

It is a figure which shows the Nishihara type abrasion test piece which evaluates abrasion resistance, (a) is a top view, (b) is a side view. It is sectional drawing of the rail head which shows the collection position of a Nishihara type abrasion test piece. It is a figure which shows the Nishihara type abrasion test piece which evaluates fatigue damage resistance, (a) is a top view, (b) is a side view.

Explanation of symbols

1 Nishihara-style wear specimens taken from pearlite steel rails
1a Nishihara type wear test specimen taken from the surface layer of the rail head
1b Nishihara-style wear specimens taken from inside the rail head 2 Tire specimen 3 Rail head

Claims (6)

  C: 0.73-0.85 mass%, Si: 0.5-0.75 mass%, Mn: 0.3-1.0 mass%, P: 0.035 mass% or less, S: 0.0005-0.012 mass%, Cr: 0.2-1.3 mass%, The balance is composed of Fe and inevitable impurities, the Mn content is [% Mn], the Cr content is [% Cr], and the [% Mn] / [% Cr] value is 0.3 or more and less than 1.0, An internal high-hardness pearlite steel rail characterized in that the internal hardness of the rail head defined by the Vickers hardness in a range of at least 25 mm depth from the surface layer of the rail head is Hv380 or more and less than Hv480. C content of the composition is [% C], Si content is [% Si], Mn content is [% Mn], P content is [% P], S content is [% S], Cr content The amount is [% Cr], the DI value calculated by the following formula (1) is 5.6 to 8.6, and the C _eq value calculated by the following formula (2) is 1.04 to 1.27. The internal high hardness type pearlite steel rail according to claim 1.
DI = (0.548 [% C] ^1/2 ) × (1 + 0.64 [% Si]) × (1 + 4.1 [% Mn])
× (1 + 2.83 [% P]) × (1−0.62 [% S]) × (1 + 2.23 [% Cr]) (1)
C _eq = [% C] + ([% Si] / 11) + ([% Mn] / 7) + ([% Cr] /5.8) (2)   When the Si content of the composition is [% Si], the Mn content is [% Mn], and the Cr content is [% Cr], the [% Si] + [% Mn] + [% Cr] value is 1.55 to 2.50. The internal high hardness type pearlite steel rail according to claim 1 or 2, wherein the internal high hardness type pearlite steel rail is in mass%.   In addition to the above composition, V: 0.001 to 0.30 mass%, Cu: 1.0 mass% or less, Ni: 1.0 mass% or less, Nb: 0.001 to 0.05 mass% and Mo: 0.5 mass% or less The internal high hardness type pearlitic steel rail according to any one of claims 1 to 3, comprising two or more kinds.   5. The internal high-hardness pearlite steel according to claim 1, wherein a lamellar spacing of the pearlite layer in a range of at least 25 mm from the surface layer of the rail head is 0.04 to 0.15 μm. rail. The steel material having the composition described in any one of claims 1 to 4 is hot-rolled into a rail shape so that a rolling finishing temperature is 850 to 950 ° C, and subsequently the rail head surface portion is equal to or higher than a pearlite transformation start temperature. A method for producing an internal high-hardness pearlitic steel rail characterized by accelerated cooling from a temperature to 400 to 650 ° C at a cooling rate of 1.2 to 5 ° C / second.

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